Fox Ranch, Malibu Creek State Park:Miniature special effects sequences were shot on the Fox Ranch.

Principal photography was completed on Sept. 11th 1974.

Trailer:

Model special effects:

The upper 15 floors of The Glass Tower was built as a facade in the dirt parking lot of the 20th Century Fox Ranch in Malibu, California, including drapes for all the windows and an explosion hole at the outside elevator track. It remained standing in the same location for many years, even after the state of California bought the land and opened the ranch to the public.

The photos below are from the excellent archive about the movie from Ryan Thoryk (with thanks).